They are not the same, especially in offensive end. Donatas' range is a little overrated. He is not a shooter, he can hit it, but he it's not his game. When people look at his Bargnani comparison, they forget about his post moves, ability to drawn fouls. That what he does.
He only has the same weak points as Bargs. Lack of defense, hustle and rebounding(motiejunas improved it a lot this season but I don't know he can put the same in the NBA)